Bonobo but not chimpanzee infants use socio-sexual contact with peers

Abstract

Bonobos have been observed to use socio-sexual behavior at higher frequency than chimpanzees. Little is known about the developmental influences that shape this behavior in bonobos. We compared the social sexual behavior of wild-born bonobo (n = 8) and chimpanzee (n = 16) infants in an experimental feeding test. Subjects of both species were orphans of the bushmeat trade living at sanctuaries in peer groups. During the experiment, chimpanzee infants never had socio-sexual interactions with one another. In contrast, bonobo infants had socio-sexual interactions significantly more than the chimpanzee infants and more often when food was presented. During these socio-sexual interactions, bonobo infants did not show a preference for heterosexual partners or genital–genital positioning that is reproductive in adults (e.g. a dorso–ventral posture). These findings suggest that the socio-sexual behavior previously observed in various captive and wild bonobos is species-typical. Wild-born bonobos originating from a large geographical range develop this behavior long before puberty and without the need for adults initiating such behavior or acting as models for observational learning. Meanwhile, chimpanzee infants of the same age with similar rearing history show no signs of the same socio-sexual behavior. Results are interpreted regarding hypotheses for the evolution of bonobo psychology.

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Acknowledgments

Thanks to Rebeca Atencia, Lisa Pharoah, Debby Cox, Keith Brown, Claudine Andre, Valery Dhanani, Dominique Morel, Pierrot Mbonzo, and the caretakers of Tchimpounga Chimpanzee Sanctuary and Lola ya Bonobo for making this research possible. This work was performed under the authority of the Ministry of Research and the Ministry of Environment in the Democratic Republic of Congo (research permit #MIN.RS/SG/004/2009) and the Ministry of Scientific Research and Technical Innovation in the Congo Republic (research permit: 009/MRS/DGRST/DMAST). This work was approved by the Institutional Care and Use Committees at Duke University. This work was supported in part by European Research Commission Advanced Grant Agreement 233297 and by National Science Foundation grant NSF-BCS-08-27552 and NSF-BCS-25172 to B.H.